In this research project, we plan to study a number of different factors that might influence the immunogenicity of the two licensed oral model vaccines, specifically the inactivated killed oral cholera vaccine, Dukoral, and the live oral typhoid vaccine, Ty21a. We will also identify strategies that might improve the immunogenicity of the vaccines. The main objective of our study is to identify immunization regimens that may improve the immunogenicity of the vaccines in young children, which could be subsequently in field trials in Bangladesh and other developing countries. Specifically, we will determine if: (i) interventions identified to enhance immune responses to Dukoral, including zinc supplementation, could also enhance the immune responses to Ty21a; (ii) these two vaccines are able to induce both acute and memory B and T cell responses, (iii) treatment with antiparasitic drugs prior to immunization could modulate the immune responses to cholera and typhoid vaccines; and (iv) examine if arsenic exerts a suppressive effect on the immunogenicity of these vaccines.